/*
 * Copyright (c) 2007, 2015, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */
/*
 * Copyright 1999-2004 The Apache Software Foundation.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.sun.org.apache.regexp.internal;

import java.io.Serializable;

/**
 * A class that holds compiled regular expressions.  This is exposed mainly
 * for use by the recompile utility (which helps you produce precompiled
 * REProgram objects). You should not otherwise need to work directly with
 * this class.
 *
 * @author <a href="mailto:jonl@muppetlabs.com">Jonathan Locke</a>
 * @see RE
 * @see RECompiler
 */
public class REProgram implements Serializable {

  static final int OPT_HASBACKREFS = 1;

  char[] instruction;         // The compiled regular expression 'program'
  int lenInstruction;         // The amount of the instruction buffer in use
  char[] prefix;              // Prefix string optimization
  int flags;                  // Optimization flags (REProgram.OPT_*)
  int maxParens = -1;

  /**
   * Constructs a program object from a character array
   *
   * @param instruction Character array with RE opcode instructions in it
   */
  public REProgram(char[] instruction) {
    this(instruction, instruction.length);
  }

  /**
   * Constructs a program object from a character array
   *
   * @param parens Count of parens in the program
   * @param instruction Character array with RE opcode instructions in it
   */
  public REProgram(int parens, char[] instruction) {
    this(instruction, instruction.length);
    this.maxParens = parens;
  }

  /**
   * Constructs a program object from a character array
   *
   * @param instruction Character array with RE opcode instructions in it
   * @param lenInstruction Amount of instruction array in use
   */
  public REProgram(char[] instruction, int lenInstruction) {
    setInstructions(instruction, lenInstruction);
  }

  /**
   * Returns a copy of the current regular expression program in a character
   * array that is exactly the right length to hold the program.  If there is
   * no program compiled yet, getInstructions() will return null.
   *
   * @return A copy of the current compiled RE program
   */
  public char[] getInstructions() {
    // Ensure program has been compiled!
    if (lenInstruction != 0) {
      // Return copy of program
      char[] ret = new char[lenInstruction];
      System.arraycopy(instruction, 0, ret, 0, lenInstruction);
      return ret;
    }
    return null;
  }

  /**
   * Sets a new regular expression program to run.  It is this method which
   * performs any special compile-time search optimizations.  Currently only
   * two optimizations are in place - one which checks for backreferences
   * (so that they can be lazily allocated) and another which attempts to
   * find an prefix anchor string so that substantial amounts of input can
   * potentially be skipped without running the actual program.
   *
   * @param instruction Program instruction buffer
   * @param lenInstruction Length of instruction buffer in use
   */
  public void setInstructions(char[] instruction, int lenInstruction) {
    // Save reference to instruction array
    this.instruction = instruction;
    this.lenInstruction = lenInstruction;

    // Initialize other program-related variables
    flags = 0;
    prefix = null;

    // Try various compile-time optimizations if there's a program
    if (instruction != null && lenInstruction != 0) {
      // If the first node is a branch
      if (lenInstruction >= RE.nodeSize && instruction[0 + RE.offsetOpcode] == RE.OP_BRANCH) {
        // to the end node
        int next = instruction[0 + RE.offsetNext];
        if (instruction[next + RE.offsetOpcode] == RE.OP_END) {
          // and the branch starts with an atom
          if (lenInstruction >= (RE.nodeSize * 2)
              && instruction[RE.nodeSize + RE.offsetOpcode] == RE.OP_ATOM) {
            // then get that atom as an prefix because there's no other choice
            int lenAtom = instruction[RE.nodeSize + RE.offsetOpdata];
            prefix = new char[lenAtom];
            System.arraycopy(instruction, RE.nodeSize * 2, prefix, 0, lenAtom);
          }
        }
      }

      BackrefScanLoop:

      // Check for backreferences
      for (int i = 0; i < lenInstruction; i += RE.nodeSize) {
        switch (instruction[i + RE.offsetOpcode]) {
          case RE.OP_ANYOF:
            i += (instruction[i + RE.offsetOpdata] * 2);
            break;

          case RE.OP_ATOM:
            i += instruction[i + RE.offsetOpdata];
            break;

          case RE.OP_BACKREF:
            flags |= OPT_HASBACKREFS;
            break BackrefScanLoop;
        }
      }
    }
  }
}
